Biomechanics Flashcards
Newton 1st law
body continues at rest or uniform velocity unless acted upon by external force
Newtons 2nd law
momentum is proportional to size of force applied and works in same direction
Newtons 3rd law
for every action is an equal and opposite reaction
Velocity =
displacement / time taken
Momentum =
Mass xvelocity
Acceleration =
( final - initial velocity ) / time taken
force =
mass x acceleration
Wind tunnels
analyse a objects AR
angualr motion
movement of a body in a circular path about its axis
measured in radians
linear motion
movement of a body in a straight or curved line
angular velocity
rate of change in angular displacement
moment of inertia
resistance of a body to change it’s rotation
MI =
mass x distribution of mass from axes
vertical forces
weight and reaction force
horizontial forces
air resistance and friction
free body diagrams -weight
originates from COM and goes down and is proportional to mass
free body diagrams -reaction force
originates from contact with ground and goes up and is equal size to weight force
free body diagrams -air resistance
originates from COM and opposes direction of motion
free body diagrams - friction
originates from all points in contact with ground and goes in direction of motion
net force
the sum of all forces acting on a body
balanced forces
occur when two or more forces acting on the body are equal but opposite in direction.
means net force = 0
unbalanced forces
occur when two forces are unequal in size and opposite in direction , a net force will be present causing the body to change it’s state
weight =
mass x acceleration due to gravity ( normally 10)
weight
the gravitational pull that the earth exerts on a body
reaction
the equal and opposite force exerted by a body in response to the action force placed upon it
friction
the force that opposes the motion of two surfaces in contact
air resistance
the force that opposes the motion through the air
streamlining
creation of smooth air flow around an aerodynamic shape to reduce air resistance
factors affecting friction : roughness of ground surface
by increasing the roughness of the ground surface friction is increased ( athlete on rubber track)
factors affecting friction : roughness of contact surface
increasing roughness of contact surface will increase friction
( athletes wearing spikes)
factors affecting friction : temperature
by increasing temp of ground and contact surface , friction is increased ( F1 tyres being warmed up )
factors affecting friction : size of normal reaction
increasing normal reaction , friction is increased
( shot putters having a high mass)
factors affecting air resistance : velocity
greater velocity , greater the air resistance
( greater velocity of sprint cyclist , greater AR)
factors affecting air resistance : shape
the more aerodynamic , the lower the AR
( cyclist teardrop helmet )
factors affecting air resistance : frontal cross sectional area
smaller the front cross sectional area , the lower the AR
( low crouched position of a skiier)
factors affecting air resistance : smoothness of surface
increasing the smoothness of a surface , AR decreases ( lycra for cyclists)
4 factors affecting AR
- velocity
- shape
- frontal cross sectional area
- smoothness of surface
4 factors affecting friction
- roughness ground surface
- roughness contact surface
- temperature
- size of normal reaction
limb kinematics
the study of movement of limbs in space , and time taken to carry out the movements
positives and negatives of limb kinematics
- can focus on a specific limbs
- can be used to improve technique
- expensive equipment
- helps prevent injury
force plates
measures ground reaction forces acting on an athlete to asses biomechanics, gait, balance and rehabilitation therapy
positives and negatives of limb kinematics
- give an immediate, accurate and reliable result
- can help improve technique
- expensive and limited access
wind tunnels
air is fired at an object to test the aerodynamics of it
positives and negatives wind tunnels
- can measure how efficient an object is so can adapt it to reduce AR
- allows tight control over environmental factors
- very expensive
- require professionals
centre of mass
the point at which a body is balanced in all directions and the point where weight appears to act from
stability
a bodys ability to resist motion and remain at rest
factors affecting stability : mass of the body
greater the mass , the greater the inertia meaning greater stability
factors affecting stability : height of centre of mass
lower the centre of mass the greater the stability
factors affecting stability : base of support
the greater the base of support , the greater the stability ( wider base or increasing points of contact)
factors affecting stability : line of gravity
an imaginary line which extends COM down to floor , the more central this line is to the base of suppor the greater the stability
4 factors affecting stability
- base of support
- height of COM
- mass
- line of gravity
2 functions of a lever system
- to generate muscular effort to overcome a load
- to increase speed of movement
4 components of a lever system
- lever ( bone)
- fulcrum ( joint)
- effort ( muscular force)
- load ( weight or resistance)
how bones act as levers
they are rigid structures that rotate around a fixed point ( joint)
the muscle that surround the joint creates the effort
classifying levers
1-2-3
F-L-E
first class lever
fulcrum is in the middle
( extension of neck when heading a football )
second class lever
load is in the middle
( plantar flexion on the ball of the foot)
third class lever
effort is in the middle - most of the levers in the body
( flexion of elbow during bicep curl)
effort arm
distance from the fulcrum to effort
load arm
distance from fulcrum to load
eg of a sport that mechanical advantage is used
having a longer tennis racket creates greater force as load arm becomes longer
mechanical advantage
effort arm is greater than the load arm so a large load can be moved with small effort
( Second class levers)
mechanical disadvantage
load arm is greater than effort arm so large effort is required to move a small load
( third class levers)
linear motion
movements of a body part in a straight or curved line where all parts move the same distance in same direction at the same time
what needs to happen for linear motion to be created
a direct force through the centre of the mass
linear motion example
skeleton and shot put
5 key descriptors of linear motion
- distance
- displacement - speed
-velocity - acceleration
-deceleration
speed =
distance / time (m/s)
acceleration =
(final velocity - initial velocity) / time taken
angular motion
movement of body or part of a body in a circular path about an axis of rotation
( measured in radians )
how many radians is 360 degrees
2 radians
how angular motion is created
eccentric force outside the centre of mass
what 3 axes does angular motion happen around
- longitudinal
- transverse
- frontal
eg of angular motion on three axis
- piroutte - longitudinal
- tumble turn - transverse
- cartwheel - frontal
3 descriptors of angular motion
- angular velocity
- angular momentum
- moment of inertia
angular velocity
rate of change in angular displacement measured in radians per s
angular velocity ( radians per seconds ) =
angular displacement / time taken
moment of inertia
resistance of a body to change its state of angular motion
( how difficult something is to move)
moment of inertia =
mass x distribution of mass from axis of rotation
moment of inertia example
a fat gymnast that’s spread out has a greater moment of inertia than a skinny gymnast whose tucked in.
To rotate quickly you need a low Moment of intertia
angular momentum
the amount of angular motion an object has
angular momentum =
moment of inertia x angular velocity
distance
total length covered from start to finish
displacement
the shortest straight line route from start to finish position
speed
rate of change in distance -
measured in metres per second
velocity
rate of change in displacement
measured in meters per second
acceleration
rate of change of velocity
measured in metres per second
distance time graph - straight line
rest
distance time graph - curved upwards line
acceleration
distance time graph - upwards straight line
constant speed
distance time graph - curved line downwards
deceleration
streamlining
the creation of smooth air flow around an aerodynamic shape
aerofoil
a streamlined shape with a curved upper surface and flat lower surface to give a body an uplift force
4 factors affecting magnitude of air resistance on a body
- velocity ( greater is greater)
- frontal cross sectional area ( larger the greater)
- streamlining and shape
- surface characteristics
projectile motion
movement of a body through the air following a curved flight path
projectile
a body that is launched into the air , losing contact with the ground surface
4 factors affecting distance of a projectile
- speed of release
- angle of release
- height of release
- aerodynamic factors
factors affecting distance of a projectile - speed of release
due to newtons 2nd law , greater force applied the greater change in momentum
factors affecting distance of a projectile- angle of release
90 degrees - projectile will accelerate vertically upwards then come straight back down
45 degrees - optimal angle
less than 45 degrees - projectile doesn’t achieve sufficient height
parabolic flight path
a flight path symmetrical about it’s highest point caused by dominant weight force of the object
( shot put)
non parabolic flight path
a flight path asymmetrical about it’s highest point caused by dominant force of air resistance on the object
(shuttle cock)
bernoulli principle
creation of additional lift force on a projectile due to higher velocity and lower pressure
lift force
an additional force created by a pressure gradient forming on opposing surfaces of an aerofoil
how lift force works
upside has a curved face creating higher velocity and lower pressure whereas the downside is straight creating lower velocity and higher pressure causing the object to be lifted
Bernoulli’s principle
creation of an additional lift force on a projectile in flight resulting from Bernoulli’s conclusion that the higher the velocity , the lower the air pressure
f1 car downforce
uses Bernoulli’s principle , curved face is on the bottom creating lower pressure and the straight face is on the top creating higher pressure , this pushes the car down
how symmetrical aerofoils create lift
by giving an angle of attack , the resulting difference in air pressure creates a lift as air has to travel further along the top side and less distance along the bottom side creating high pressure underneath.
magnus effect
creation of an additional magnus force on a spinning projectile which deviates from the flight path
magnus force
a force created from pressure gradient on opposing surfaces of a spinning body moving through the air
hook
a type of side spin used to deviate a projectiles flight path to the left
slice
a type of side spin used to deviate a projectiles flight path to the right
top spin
a type of spin creating a downwards magnus force , shortening the flight path
back spin
a type of spin creating an upwards magnus force , lengthening the flight path
how spin creates a pressure difference
the side of the ball spinning that’s opposing the direction of motion creates a higher pressure making the ball move to the opposite direction to this
